A number of applications have been developed for oleic acid in the fields of cosmetics, textiles, metalworking chemicals, and corrosion inhibitors. As used herein the term "oleic acid" is intended to mean a cis-9-octadecenoic acid; a monounsaturated C.sub.18 fatty acid which is a common component of almost all naturally occurring fats as well as tall oil. Currently, most commercial oleic acid is derived from animal tallow or natural vegetable oils.
Tall oil consists of a mixture of fatty acids, resin acids, and various neutral components (e.g., hydrocarbons, resin and wax alcohols, sterols, esters, and residues). About 40 to 50% of the fatty acids contained in tall oil is oleic acid, while another 35 to 45% is linoleic acid (9,11- or 9,12-octadecadienoic acid). It has been known to fractionally distill tall oil since the early 1900's. However, due to the structural similarities between oleic acid and linoleic acid, additional refining steps have been necessary to separate (and purify) these two acids.
One such separation method is the Emersol process described in U.S. Pat. No. 2,421,157 to Myers et. al., which uses methanol as a solvent. The fatty acid source is mixed with anhydrous methanol and the subsequent solution is subjected to low temperatures and filtered to extract the oleic acid. A similar solvent process is taught by Gee in U.S. Pat. No. 2,450,235 where acetone is employed as a solvent in place of methanol. Both of these processes depend on NH.sub.3 refrigeration to cool the solvent fatty acid mixture and can be very costly.
Another method of producing oleic acid is based on the use of molecular sieves to separate the different fatty acids, as evidenced by U.S. Pat. Nos. 4,529,551 to Cleary et al., and 4,534,900 to Cleary. Two of the drawbacks to these processes are the need to use two solvents for the separation and the problem of the molecular sieve "filter" becoming clogged with trace contaminants.
Other known methods of separating oleic acid include: a methyl formate solvent process (U.S. Pat. No. 3,755,389 to Blaney), an air entrainment process (U.S. Pat. No. 3,953,484 to Sutker), a lithium soap separation process (U.S. Pat. No. 4,097,507 to Person), and a urea separation process (U.S. Pat. No. 2,838,480 to Swern et al.). Although promising, none of these processes has yet been commercialized on a major scale.
Therefore, it is the object of this invention to provide a process for producing high-purity, light color oleic acid. Other objects, features, and advantages will be evident from the following disclosure.